shell: Set state_changed when we make a surface transient

If we don't mark the state as changed, we don't copy over next_state to
state and we fail to treat the surface as a transient.  In particular,
we give it a random intial position instead of mapping it at the given
parent relative position.

https://bugs.freedesktop.org/show_bug.cgi?id=72532

desktop-shell/shell.c

@@ -2158,6 +2158,7 @@ set_transient(struct shell_surface *shsurf,
 	shsurf->transient.flags = flags;
 
 	shsurf->next_state.relative = true;
+	shsurf->state_changed = true;
 	shsurf->type = SHELL_SURFACE_TOPLEVEL;
 
 	/* The layer_link is updated in set_surface_type(),